This invention relates generally to magnetic disk drive systems, and more particularly to methods and apparatus for the detection of interference between the head and recording disks of a head/disk assembly in such systems.
In typical magnetic disk drive systems, where the recording disk moves relative to the head, it is usually desirable to space the head close to but not in contact with the recording disk. This close spacing is particularly important in systems where the recorded data is in the form of magnetic bits, since the spacing between the recording disk and the head determines the maximum bit density and hence the storage capacity that can be achieved. Conversely, continuous or intermittent contact between the head and the recording disk produces undue wear, the accumulation of dirt and results in the degradation of the recorded signal.
It is well known that the rapid relative movement of the recording disk and the head generates a laminar air flow or gas fluid layer between them. The rapidly moving fluid layer may be used to cause a head to "fly" or float at a given distance above the recording disk, the prior art being replete with methods by which a head may be caused to "fly" by utilizing a fluid bearing. However, many problems are encountered in devising practical fluid bearing means for controlling the relative position of a head and a recording disk, the relative speed of the head and recording disk in some cases being too low for sustaining a fluid bearing. Alternatively, a high relative speed may make such arrangements susceptible to acceleration forces that can be induced by vibrational and positional changes.
It is clear that systems which must rely on fluid bearing arrangements, for relative positioning of the head or heads, are susceptible not only to erratic positioning of the head or heads, but also undesirable "crashing" of the head or heads on the surface of the recording disk. Furthermore, unless special precautions are taken, there is deleterious rubbing contact between the head and the recording disk while starting an stopping the apparatus. Such rubbing contact is especially susceptible in recording disks having "asperities" or irregularities in their surfaces.
There are many quality control arrangements, both in the production of magnetic disk drives and in the production of the recording disks themselves, to determine whether the disk drive or disk is susceptible to interference therebetween during operation of the head/disk assembly. However, no such simple arrangement exists in the prior art for the detection of head/disk interference in the field.